Containers such as bottles are conventionally filled by one of two types of machines. In straight filling machines, a plurality of bottles is carried along a conveyor belt down a straight path and a plurality of filler heads contact the top of the bottles by moving downwardly and horizontally along with the bottles. Once a filler head is secured on a bottle, liquid is fed into the bottle through the filler head from one or more reservoirs, with filling continued either for a fixed time or until a certain level has been reached, generally by the sensing of overflow from the bottle.
In the second type of filling machine, bottles are received one at a time onto a rotary device, frequently by lifting each bottle individually up to a filler head. While contact is usually made between the bottle neck and the filler head or an aligning collar attached to the filler head, in some cases no such contact is made. The bottle and filler head then travel together along a circular path while liquid is fed into the bottle. Again, completion of filling is usually sensed by overflow.
A series of machines manufactured by Pneumatic Scale Corporation employs a back pressure sensing means for determining that a desired level has been reached in the bottle. In those machines, an aligning collar aligns each bottle on a straight conveyor or a rotary star wheel under a filler head, the filler head moves downwardly into the bottle, and the flow of liquid commences. When the desired level is reached, back pressure is sensed by a "low pressure" gas flow and, simultaneously, the liquid flow ceases and the filler head retracts upward from the bottle.
All of the above bottle filling machines employ moving parts above the level of the bottle neck. It is important, however, for some applications such as semiconductor processing that chemicals be available with extremely low particulate contamination counts. The use of conventional bottle filling machines to package such chemicals introduces particulate contamination into the bottles either because of particulates generated when an adjusting collar or other device contacts the bottle neck or by movement of machinery parts associated with the filler head.